docs: def pdf_Rosin_Rammler(d, k, m):
      r'''Calculates the probability density of a particle
      distribution following the Rosin-Rammler (RR) model given a 
      particle diameter `d`, and the two parameters `k` and `m`.
      
      .. math::
          q(d) = k m d^{(m-1)} \exp(- k d^{m})
          
      Parameters
      ----------
      d : float
          Specified particle diameter, [m]
      k : float
          Parameter in the model, [(1/m)^m]
      m : float
          Parameter in the model, [-]
  
      Returns
      -------
      pdf : float
          RR probability density function, [-]
  
      Notes
      -----
  
      Examples
      --------
      >>> pdf_Rosin_Rammler(1E-3, 200, 2)
      0.3999200079994667
  
      References
      ----------
      .. [1] Rosin, P. "The Laws Governing the Fineness of Powdered Coal." J. 
         Inst. Fuel. 7 (1933): 29-36.
      .. [2] Bayat, Hossein, Mostafa Rastgo, Moharram Mansouri Zadeh, and Harry 
         Vereecken. "Particle Size Distribution Models, Their Characteristics and
         Fitting Capability." Journal of Hydrology 529 (October 1, 2015): 872-89.
      '''
      return d**(m - 1.0)*k*m*exp(-d**m*k)